Vaseline, Silglyde, or white lithium grease usually. If I'm doing hydraulic work I use the fluid that's in the system unless it requires something more like grease.
I've always used motor oil for most O-rings, and soapy water or coolant for cooling system ones. For AC ones, I've used Nylog or the same oil for the compressor.
Originally Posted by dlundblad
What does everyone use? Installing things like injectors "dry" doesn't work.
I have used a small amount of engine oil if the o rings are for the injectors. Gas and oil will not harm injector o rings. Obviously, this doesn't apply to all o rings. I would not use silicon grease anywhere near fuel or air intake.
Depends on application. As mentioned motor oil for injectors. I have used silicone oil, silicone grease and nyogel for others. Super lube usually works well. Many nitriles wil handle tour choice of petroleum lubes just fine.